Cowboy Rocketship
Grasshopper Hovverslam (with Video and Johnny Cash)
“SpaceX’s Grasshopper doubled its highest leap to date to rise 24 stories or 80.1 meters (262.8 feet) today, hovering for approximately 34 seconds and landing safely using closed loop thrust vector and throttle control. Grasshopper touched down with its most accurate precision thus far on the centermost part of the launch pad. At touchdown, the thrust to weight ratio of the vehicle was greater than one, proving a key landing algorithm for Falcon 9. Today’s test was completed at SpaceX’s rocket development facility in McGregor, Texas.”
Keith’s note:
The image to the right is the best one I could find of the cowboy that stands on the deck of the Grasshopper. You can see it at the end of this video for a few seconds. SpaceX PR folks did not have anything better to offer me. When you enlarge this video frame grab you can see that the SpaceX cowboy bears more than a passing resemblence to Guy Fawkes. I’m just sayin’…
Impressive, especially in light of reports on NSF that the F9 v1.1 maiden flight booster will attempt a turnaround and water touchdown on its maiden flight. If they manage to pull that off it’ll be a major step to an RLV – and cause a major geek-gasm.
Doc:
A link to that would be much appreciated. 🙂
tinker
This March 7 info set it off, and since then the SpaceX General, Grasshopper, RLV etc threads have exploded. It even leaked into the CRS2 mission thread. For a while page turnovers were about every 30 min.
http://forum.nasaspacefligh…
Later posts reported that GH2 is on the short list, and will fly from White Sands to 300,000 ft. Just a couple –
http://forum.nasaspacefligh…
http://forum.nasaspacefligh…
More tidbits surround these.
🙂 so so wonderful to see progress to affordable space flight.
Spacex Fanboy
The thrust to weight ratio greater than one at touchdown suggests the rocket was still decelerating at the moment of touchdown. SpaceX is well aware that to minimize fuel consumption a vertical lander has to slow its descent at the last possible moment.
True for a single rocket engine with fixed throttling ability (70% for the 1D, I believe). But there’s no law against using multiple, throttlable engines at different points in the descent profile, nor against designing and installing at least one engine with very deep throttling. You can bet that the folks at SpaceX are smart enough to have considered all of this.
Folks:
As SpaceX expands the envelop with Grasshopper from the ground up, expect them to play with their expended first stages from the top down. This way, they work on both ends of the flight profile at the same time. When the numbers meet reality somewhere in the middle, they’ll have the data they need to build and fly a reusable first stage.
V4
The most efficient vertical powered landing profile is to drop til the last minute then decelerate at full thrust. Scary for a crewed spaceship but for a booster stage, maybe it’s the only way to ‘close the loop’, as Elon likes to say.
tinker
Yup, numbers are pretty scary for a T/W>1 landing of a reusable rocket. The engine throttle range and the rocket’s terminal velocity during descent will determine the time interval available to restart the engine so that it can safely land, but it’s safe to say it will be on the order of a (very) few seconds either way. And then it’s just a few tens of seconds from terminal velocity (close to 100m/s) until landing.
For a high enough T/W (say, 2) we could be talking of decelerating the stage of a rocket from terminal velocity down to a standstill starting at below 500m(!) altitude… Now *that* would be something!
As non rocket guy, no clue what you just said??
Depending on the angle of flight after booster turn around doesn’t drag in the atmosphere play a factor in slowing the booster. Will they bring the boosters down ranger velocity to close to a stand still before dropping in to thick atmosphere??? When a person sky dives doesn’t the atmosphere slow them to about 200 miles/hour anyway????
Just trying to understand.
Help!!
Joe Q
First of all, sorry for the jargon.
To answer your question: the first stage of Falcon 9 will be flying too fast when it separates from the second stage (something like Mach 9), so it will probably just burn up during descent if it doesn’t brake a little at high altitude. The atmosphere will then do the rest of the braking down to terminal velocity (which may well be very different than those 200mph you mentioned for that rocket).
Also, at landing a single Merlin engine is supposed to be restarted. Problem is, the engine cannot throttle below 70% of full thrust, so with an empty rocket, the two options are essentially no brakes, or full brakes.
So the rocket will have to wait until the last possible moment before restarting the engine (this could happen well below 10 000 feet), then will brake at almost full thrust to land exactly at zero velocity.
Both engineering-wise and non-engineering-wise, if the guys at SpaceX can pull it off, that will be quite a feat…
So if it can’t throttle below 70%, what happens when it manages to stop above the ground? I guess they just can’t do that. It gets one go and they have to throttle it right the first time. …. ah this is assuming that 70% thrust gives positive vertical motion. I guess that depends on the thrust/weight ratio at the time.
You fire up the turbo fan engines, deploy the wings and fly that booster horizontally back to the launch site, right Steve!!! Lolololol
Hard headed
🙂
DTARS:
What he said: With a little more thrust then you weigh, it would take less then a minute to go from free falling to dead stop (Hopefully at the same time your reach the ground). In Grasshopper’s case, they were still going down while the Merlin was pushing more then the ships weight, decelerating as it went. If they needed to hover, they have less throttle range to cover then if the pushing less then their weight at a constant decent rate. Almost like pushing on a spring to give you an idea.
The second part is what if you pushed with twice the thrust of your weight? You’d need less height and time and use less fuel too but there is no time for second chances. Imagine Grasshopper free falling to half a mile altitude, then, ‘ffffFFFFFFFFFFT, SLAM … … … … clonk!’, there sitting pretty on the landing pad in 20 seconds flat! See? It’s a scary solution but, as Elon says, “…it closes.”.
Hope that helps:
tinker
Propellant is useful only when it changes velocity. Once the rocket is descending vertically, every second the engine burns to fight gravity rather than decelerate is lost propellant. Hovering will quickly leave it out of fuel. To make vertical landing feasible the engines must fire at the last possible moment and produce the greatest practical acceleration, and the rocket must come to a stop just as it touches down, so timing is critical
Thanks gentlemen
There is an additional reason why they would start testing with expended first stages: as their Grasshopper flights start flying higher and faster, the risk of damage to the vehicle at landing becomes greater.
Once SpaceX shows it is able to safely bring the rocket’s first stage back down to the lower atmosphere, it may become a lot less risky for them to just perform landing attempts with their expended first stages than with the Grasshopper.
Congratulations Space X.
Wow. Tesla, Space X and SolarCity. Musk seems to be on a roll these days.
Hopefully he keeps Space X private for a good long time. We seem so failure averse these days, I doubt any publicly traded space company could survive the formative years.
Recently, I happened to see a new profile of Pixar on Bloomberg. Chief creative officer John Lasseter mentioned that failure was PART of the Pixar culture. He surrounds /supports his employees’ experiments/efforts with safety nets made of pillows, etc.
Experimentation and risk is good at Pixar and is exactly opposite of the Hollywood culture, where a fall is met with knives and pitchforks, rather than a safety net.
I wonder what it would take to see risk followed through to complete in the Big/Arsenal Space Community? Last time I saw a vertical landing from a Major player was DCX back in the 90’s.
Yo, Keith, howdy pardner…
I don’t think Elon (or whoever had that cool inspiration) had Guy Fawkes in mind — especially given the flavor of the soundtrack.
This is definitely more in tune with the Late Great Mr. Cash…
a.k.a. (his handle): The Man In Black (or should I say Man(nequin).
Jus’ say’n.
=]8})
I still think it could catch a gantry with a hook on the top and avoid the ground effect and the need to carry landing gear….
Stuart:
Brilliant idea! Just have the booster come down at an angle instead of straight down. You could even have an active boom swing into place and target the hook on the nose. Have it over water ‘just in case’.
That tells me you’ve just invented the barge mounted landing hook. Have your catch crane at one end to catch the booster over water then transfer it to horizontal on the deck. It doesn’t have to be too far off shore from the launch site either, just in deep enough water for a booster not too bottom out if they miss. That would turn a bad day into a not so good day with no crater.
If SpaceX can hit their concrete pad in the center at zero velocity then they should be able to hit a target above ground with the same accuracy. Not having landing legs would be a big weight savings.
Any show stoppers here, folks? Other then limiting landing places to where there are ‘Gauntlet Barges’ (they are catching Falcons after all), I see no caveats. For the first stage, this isn’t a problem because they intend it to land near the launch pad. For the second stage, I don’t think the weight of the landing gear is as much of a burden and being able to land ‘anywhere’ would make for more flexible scheduling. Landing a reusable Falcon second stage anywhere in America puts it only a few days away from the launch site by truck.
Have I missed anything (as ususal:))?
tinker
Get blown ten feet that way at the last second and you are out of reach of the arm. Get blown ten feet that way at the last second and you just smashed into the gantry.
Paul:
Problems, problems. Yes, very true. But is it still worth developing for the weight savings? There’s no hurry either. Put landing legs on the first ones and practice, practice, practice. If they get the kinks out enough to feel comfortable with hook landings then they can advance the design and gain a major performance improvement.
tinker
Rockets are designed to be strong in compression, not strong in tension. Suddenly suspend the stage from its top end with all the weight of the engines at the bottom, and you could end up tearing tank welds open…
Duncan:
That’s the show stopper I was looking for. If they have to add weight to hang the stage from it’s top there’s no real mass gain over landing gear.
How about catching it at the thrust frame on the bottom of the stage. All it has to do is set still in the air for a few seconds for active grapples to connect on either side like pincers.
tinker
You’d be trying to catch it in the same king of cradle you launched it from. (With some extra attachments & reinforcing to deal with an imperfect grab.)
And remember, the finer control you need for capture, the longer that final manoeuvre takes (the longer you spend in hover, trying to line up just-so), the more fuel you are burning, the more reserve you need to carry for the rest of the flight… the less benefit you get from just sticking four legs on it and landing on a big open concrete pad.
Paul:
You mean some kind of launch/landing table. Have a guide cone for the last bit of error like the Shuttle’s docking ring but on the ground. How about a pedestal above the ground like SpaceX’s cool test stand in Texas. You can’t get more rapidly reusable than landing on your launch pad. A simple, lowest common denominator solution. I like it.
But can it be done? Land a rocket with the accuracy of a Shuttle/ISS docking every time? If so, it sounds like a good compromise between weight savings vs. complexity.
Hmm…
tinker
The operational F9R won’t be able to hover, because it won’t be able to throttle down to T/W ~ 1.
And what if the stage has to abort to an alternate landing site due to bad weather? Are you going to load the capture equipment in the back of a truck and chase it? The F9R first stage with landing legs can land in a parking lot if it needs to.
Duncan, oe the spacex website falcon 9 processing pictures, it shows the entire falcon 9 first stage being supported horizontally by only two supports: one at the engines, and one at the interstage. If the first stage can support all of the weight horizontally being held only on each end (no strongback), then it can probably handle tension.
http://www.spacelaunchrepor…
Scroll 1/4 down
Folks:
Meanwhile, back at The Cape, folks are having a ‘Karl Rove Moment’, still thinking they can attract SpaceX to Florida:
http://www.floridatoday.com…
It’s worse than they think too. SpaceX will probably abandon their launch site at Canaveral AFB as soon a it’s feasibly possible. There is no advantage to SpaceX having two launch pads at The Cape, let alone one.
tinker